Various types of line trimmers are presently known and are being marketed in the vegetation cutting art. These trimmers generally include a handle or other means by which the device can be transported and guided during use. Mounted to the handle, near one end thereof, is a cutting head. The cutting head typically includes a protective shield having mounted therein a filament holder which can be made to rotate about a substantially vertical axis.
Line trimmers known in the art often use one flexible filament cutting element extending from the filament holder generally radially with respect to the axis about which the filament holder rotates. When the filament holder is made to rotate about its axis of rotation, the filament cutting element generally defines a plane perpendicular to the axis of rotation. Heavier duty line trimmers sometimes incorporate a plurality of single filament cutting elements, individual elements being positioned at equal angular distances about the filament holder. When such additional filament cutting elements are utilized, all cutting elements tend to rotate about the filament holder's axis of rotation in the same plane.
It is also known to coil a length of filament about the filament holder so that, as that portion of the filament length being used for trimming becomes worn, a new length may be metered out. This metering operation can be accomplished in devices utilizing multiple angularly spaced cutting elements.
Typically, filaments having a cross-sectional diameter of approximately 0.090 inches are currently used in line trimmers. It has been recognized that, by reducing the filament's diameter yet maintaining a speed of rotation of the filament the same as that at which a 0.090 inch filament is made to rotate, the cutting effectiveness of the element can be improved. This is true since, by reducing the area over which a constant force is applied, the amount of force per unit area is increased. The effectiveness of a thinner cutting element is greater than one having a larger cross-sectional diameter for the same reason that a sharp knife is more efficient than a dull one. Application of a certain force to the sharp blade will be distributed over the area of the cutting edge so that the force per unit area is greater than it would be if the knife were dull.
Another disadvantage of cutting elements using single filaments of approximately 0.090 inches in diameter as opposed to smaller filaments is that when they break off in operation, they tend to be more noticeable on a ground surface as debris.
Despite this, it has been thought less than optimum, however, to reduce the diameter of the cutting filament below 0.060 inches. This belief is based on the conclusion that to do so would decrease the strength of the filament and, commensurately, permit increased frequency of filament deterioration.
The invention of this application is intended to overcome the above shortcomings by providing a cutting element with a high force per unit area to cut grass sharply and effectively without as much bruising as is typical with larger cutting elements, yet to provide a cutting element which is less noticeable as debris on a lawn surface when breakage of the filament occurs. Further, it is intended to provide these advantages without significantly increased frequency of cutting element replacement.